Helium is pumped into a spherical balloon at a rate of 3 cubic feet per second. How fast is the radius increasing after 3 minutes?
I know . but i don't know how to find the radius of the balloon at 3 minutes.
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Convert the "three minutes" into seconds, and find the volume after that number of seconds.
Plug this volume into the "volume" formula, and solve for the radius at that time.
Differentiate the "volume" formula with respect to time. Plug in the known values for and , and solve for .